CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- The Boolean AND operation:
1st Bit 2nd Bit Operation Result
0 0 AND 0
0 1 AND 0
1 0 AND 0
1 1 AND 1
- The bitwise Boolean AND operation between an IP address and its subnet mask is used to
discover the subnet number for the IP address.
- First address Add 1 to the 4th octet of the subnet number.
Broadcast address Change the values of all host bits in the subnet number to binary 1s.
Last address (or largest valid IP address) Broadcast address – 1.
- Example 1: 10.0.0.1/16
IP Address 10.0.0.1 00001010 00000000 00000000 00000001
Subnet Mask 255.255.0.0 11111111 11111111 00000000 00000000
Subnet Number 10.0.0.0 00001010 00000000 00000000 00000000
First Address 10.0.0.1 00001010 00000000 00000000 00000001
Broadcast Address 10.0.255.255 00001010 00000000 11111111 11111111
Last Address 10.0.255.254 00001010 00000000 11111111 11111110
- Example 2: 172.16.0.1/24
IP Address 172.16.0.1 10101100 00010000 00000000 00000001
Subnet Mask 255.255.255.0 11111111 11111111 11111111 00000000
Subnet Number 172.16.0.0 10101100 00010000 00000000 00000000
First Address 172.16.0.1 10101100 00010000 00000000 00000001
Broadcast Address 172.16.0.255 10101100 00010000 00000000 11111111
Last Address 172.16.0.254 10101100 00010000 00000000 11111110
- Example 3: 192.168.100.100/28
IP Address 192.168.100.100 11000000 10101000 01100100 01100100
Subnet Mask 255.255.255.240 11111111 11111111 11111111 11110000
Subnet Number 192.168.100.96 11000000 10101000 01100100 01100000
First Address 192.168.100.97 11000000 10101000 01100100 01100001
Broadcast Address 192.168.100.111 11000000 10101000 01100100 01101111
Last Address 192.168.100.110 11000000 10101000 01100100 01101110
- Total number of subnets 2 n – 2, where n is the number of subnet bits. [1]
Total number of hosts 2 n – 2, where n is the number of host bits. [2]
[1] minus the subnet zero and the broadcast subnet.
[2] minus the network address (all-0s bit pattern) and the broadcast address (all-1s bit pattern).
Subnet zero It has all binary 0s in the subnet portion. Also known as all-0s subnet.
Broadcast subnet It has all binary 1s in the subnet portion. Also known as all-1s subnet.
- Ex: In 172.16.0.0, 255.255.255.0, 8 bits are borrowed from the 16 host bits for subnet bits.
With these 8 subnet bits, there are 2 8 – 2 = 254 subnets, and each subnet has 8 host bit, which are
2 8 – 2 = 254 hosts are available on each subnet.
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com